Biomarkers are incorporated into cross-sectional, case-control and prospective cohort studies of occupational causes of cancer in order to enhance exposure assessment, provide insight into early biologic effects of specific chemicals, evaluate sources of genetic susceptibility and classify tumors at the molecular level to identify subgroups that may be more etiologically homogenous. Ongoing and planned cross-sectional studies include populations exposed to benzene, chlorinated solvents, disinfection byproducts. polycyclic aromatic hydrocarbons, arsenic, and selected pesticides. On-going case-control studies of stomach, esophagus, brain, bladder, renal cell and breast cancer, NHL, and benzene-induced hematotoxicity and hematologic malignancies and cohort studies of women in China and agricultural workers in the United States are evaluating a range of potential genetic risk factors and their interaction with occupational and environmental exposures. Many of these studies are also collecting tumor samples for future molecular analyses.